The invention relates to a process for producing a fiber optic cable, or an assembly element for a fiber optic cable.
A process for adjusting the excess length of a fiber optic cable, which contains at least one optical fiber, in relation to a sheath in the form of a metal tube is disclosed in DE 39 10 122. The metal tube is drawn through a bending apparatus for plastic deformation and is subsequently straightened again. The idea underlying this publication is that the limit of longitudinal elastic deformation is substantially higher under tensile load than under compressive load. Thus, in the outer curvature area, the metal tube is deformed only elastically, but in the interior also plastically with the result that the straightened metal tube is shortened. The excess length that can be achieved with this process is limited to less than 0.3%.
DE 40 03 311 discloses a process for producing the excess length in which the strip to be formed into the tube, or a certain tube segment, is reversibly elongated and the optical fibers are inserted into the tube thus being formed in the region of the elongated tube segment. The metal strip or tube segment is heated to above the ambient temperature and finally cooled, which causes the tube to become shorter. This process, too, does not permit excess lengths of more than 0.3% since too much heat would damage the optical fibers.
DE 42 10 633 discloses a process for producing excess length in which the metal tube containing the optical fibers is upset and thus plastically shortened, so that the optical fibers lie in the upset metal tube with a defined excess length. Although this process permits excess lengths of between 1% and 8%, the cost involved is substantial, so that it is practically excluded for cost-effective production.
Finally, DE 44 34 133 discloses a process for producing a fiber optic cable in which the excess length of the optical fibers is produced by placing the metal tube around a capstan in at least one turn. The force applied by the capstan to the metal tube causes an elastic deformation of up to 0.6%. The elastic elongation of the metal tube is cancelled out on the capstan.
The object of the invention is to provide a process for producing a metal tube containing one or more optical fibers making it possible to obtain almost any adjustable excess length of the optical fibers relative to the metal tube.
This object is obtained by a process and device according to the present invention, the features of which are set forth in more detail below.
Advantageous further embodiments of the invention are set forth in the dependent claims.